I surmise that since you have a farm this big......you do own equipment such as front end loader and skid steers. The material will decay and cause immense heat....and smoke. The piles will need to be turned once every other day.
The reason of possible sudden flash fires with dead grass is the problem. I can understand manure's mixed with topsoil will hasten fires, but with pulverized leaves, grass clipping.....the heat can cause a flash fire.
This is the only reason for our EPA will not allow such sites unless you are well equipped to handle the work load.